1. Field of the Invention
The invention relates generally to concrete additives, and more particularly, to methods and compositions for improving air entrainment in cementitious mixtures.
2. Background Information
There is a growing demand for concrete in building and construction applications. The entrainment of air in cementitious materials, for example, Portland cement, concrete, mortar, and grout, is beneficial for providing resistance to cracking when the materials are subjected to cyclic changes in temperature conditions.
Air entrainment agents (AEA) may be added to cement-based mixtures to entrain microscopic voids of air in the mixture. The voids may measure from 10 microns to 250 microns in diameter. The presence of the voids is believed to alleviate internal stresses caused when moisture freezes within pores inherently formed during setting of the cement. In harsh weather locales where an air entrainment agent is needed, there may be up to ten percent (10%), by volume of the cement, of air entrained within the voids. It should be understood that as air content increases, the compressive strength of the cementitious materials is lessened.
The demands of industry require that concrete be of sufficient strength and durability. The addition of the air entraining agents results in an improved durability as the result of entrained air voids. The voids may be stabilized by the action of the surfactant-based air entraining agents, and the voids help to relieve the expansive forces encountered when water freezes within the void.
A need remains for a method for improving air entrainment for cementitious mixtures and concrete.